The present invention relates to an optic device that enables an observer to look at what is normally in his field of vision and, simultaneously, at a collimated image, through the introduction of this image into his visual field, using an image-combining optic system that includes at least one semi-reflecting mirror. It must be noted that, in this document, the term "collimated image" refers to an image formed at infinity: the fact of giving the observer a collimated image prevents him for having to adjust his eyesight in different ways when he focuses his attention on the outside view and when he focuses it on the image, thus averting eye fatigue.
Such optic devices exist. They ar used especially in aeronautics, for example to provide a pilot with piloting information without obliging him to take his eyes off the outside view.
Thus, the European patent No. 0077 193 describes a first optic device comprising a block of transparent material with two plane, parallel and polished faces and one input face, and a semi-reflecting spherical mirror within this block. This block is made so that an incident ray coming from an image generator, after going through the input face, undergoes a total reflection on one of the two parallel faces, then a partial reflection on the semi-reflecting mirror, then a refraction on that face of the two parallel faces on which it has already undergone a total reflection. The light rays coming from the scene to be viewed go through the optic block by the two parallel faces and the spherical mirror before reaching the observer's eye. This optic device has two drawbacks in particular: the transparent block is thick and, therefore, heavy and bulky, and the input face forms a mask that reduces the observer's visual field.
There is also a known way, disclosed in the French patent application No. 89 06721, of using an image generator and a sequence of parallel, semi-reflecting mirrors positioned in an optic waveguide and processed to be reflective at incidence values that get increasingly smaller with distance from the generator. The observer looks at the outside view by transparency through the semi-reflecting mirrors. This second optic device, which shall be represented by FIG. 1 appended hereto, has certain drawbacks. These drawbacks include, more especially, the fact that it has a pupil for the injection of images into the optic system that is about thirty millimeters high and is therefore too big, and that it is subject to parasitic reflections due to reflection on the edge of the optic waveguide.